Two helicopters collided in the air over Rio de Janeiro in the morning, killing six people and turning a routine flight into a fast-moving disaster in the city’s southwestern part. One of the aircraft detonated when it hit the ground, and flames then spread to electric vehicles, triggering new explosions.

The crash matters today because the damage did not stop with the impact. Fire and blasts widened the scene, while the second helicopter came down on the grounds of an abandoned church rented by BYD, a detail that puts the wreckage in the middle of a commercial property as well as a rescue site.

According to the National Agency of Civil Aviation, one of the helicopters was a Eurocopter AS 350 B2 that had been in use since 2012. That leaves the central question unanswered: what caused two aircraft to collide in midair at all. The available facts do not explain whether the dead were occupants of both helicopters or whether anyone on the ground was among them, only that six people received injuries incompatible with life.

The wreckage also carries a complication that matters for any accounting of the deaths. One helicopter exploded on impact and the fire spread into parked electric vehicles, so the final toll may reflect not just the collision itself but the chain reaction that followed when the aircraft reached the ground.

This was not the only helicopter crash mentioned in the background, either. A Robinson R44 crashed during takeoff at North Perry Airport in Florida and four people were injured when it overturned after the fall and struck a nearby airplane. The comparison underlines how quickly a helicopter accident can spread beyond the aircraft itself once control is lost.

For now, the day ends with six dead, two helicopters destroyed and no explanation for why the collision happened. What remains unknown is the piece that would turn a catastrophe into a complete account: whether the deaths came from the midair crash, the ground explosion or both.